Improved flow through the Halfweg Locks

The flow at the site of the former lock complex at Halfweg (Haarlemmermeer) needs to be improved considerably. When heavy rainfall threatens to flood the polders, several pumping stations are put into operation. However, the supply of sufficient water at the former lock complex is a significant obstacle because the complex forms a bottleneck in the water’s path. Because the locks at Halfweg do not allow enough water to pass through to the Boezem pumping station, the water level in this section (side canal F) drops too much, causing localised flooding. Due to the lack of water supply, the Boezem pumping station cannot function optimally and even has to be shut down in some situations. Iv created the preliminary design for improved flow based on the architectural design of TAK Architects.

Improving the flow of water in a historic part of the Netherlands means making the most of an area the size of a postage stamp. The lock complex is a municipal monument, which posed a challenge to improving the flow. A new passage will be dug to improve the future situation and the flow of water from the polder. This passage will be realised in the eastern lock island of the historic lock complex. New sheet pile walls will provide additional structural strength. An underwater concrete floor will function as a support for the sheet piling. The aim is to achieve improved flow without affecting the island’s current appearance and preserve its monumental value. For example, the lock and wing walls will be restored, and the sandstone capstones of the western and eastern islands will be restored as much as possible.

Integrating a large civil engineering structure into a monument is complex, not only because of the fragile environment but also because the surroundings take a very critical view of it. The only way to achieve this is to improve and beautify the structure and all the functions. Together with TAK Architects, we have done this very well. The preliminary design considered in detail the risks during the works, with the poor condition of the locks and feasibility being the biggest concerns. The preliminary design, therefore, included detailed attention to the foundation, soil protection and infrastructure.

Getting the plans approved by the Heritage Committee of Haarlemmermeer Municipality was a challenge that required the support of all stakeholders. This experience led to valuable insights, especially in the cooperation between engineering, restoration and collaboration with the architect.

Improving the flow will increase water drainage from the southern polders – on the Boezem side – and enhance the inflow to the Halfweg pumping station behind it. This is essential to ensure dry feet in the area, which is the responsibility of the Rijnland District Water Control Board. All this work will result in an improved public layout of the entire lock complex. Cyclists passing through the lock complex will soon be able to admire all the historical elements of the past. The route of the ‘late’ railway line (the first in the Netherlands, the Amsterdam – Haarlem railway line from 1839) is visible through the use of alternative materials (sedum instead of grass), and two benches are a tribute to the former passages of the lock.